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Re: libguile and readline


Karl Franz Fogel wrote:
> 
> Maciej Stachowiak <mstachow@alum.mit.edu> writes:
> > Who is violating the GPL in this situation? There are three parties
> > involved, the user loading the library at runtime, the author of
> > the GPL'd library, and the author of the proprietary application.
> > [... the expected expansion followed... ]
> 
> Perhaps we are seeing things too narrowly for legal purposes here, by
> evaluating legality in purely technically terms.
> 
> Clearly, any library with a stable API can be linked in at run time by
> a user running a proprietary application (assuming the application is
> compatible with the API).  If the author of that application was
> helpless to prevent this choice, then she obviously cannot be in
> violation of the GPL.
> 
> However, if the application is designed in such a way that it is not
> truly functional until a certain specific GPL'd library (say, Guile)
> is linked in, and the application's users are explicitly expected to
> do so, then Guile is effectively a part of the application even though
> they were not distributed together, and the proprietary application is
> violating the GPL.

The library I was thinking of in this case is not Guile, which is GPL with
a special exception that linking against it does not subject a program
to the GPL, so linking it into a proprietary app is legal in any case. What 
I was thinking of was a GPL'd Guile extension library that is not required
for the proprietary app to run, but will enhance the functionality of the
app's Guile interpreter if loaded by the user. In particular, I was
thinking of a GPL'd library that provides a Guile interface to readline,
but is separate from libguile. If an application linked against Guile
without causing the readline extension to be loaded by default, then all
would be kosher license-wise. If, however, a user chose to load the
readline extension into the proprietary application's Guile interpreter
as a convenience, I think this would _still_ be legal, as I read the GPL,
since there is no dependency between the app and the readline module, and 
the user is not distributing.

Of course, IANAL as well, and even if I were, there'd be no court precedent
on the GPL to go by.

 - Maciej Stachowiak